CHAPTER 3 Air Quality CHAPTER 3: AFFECTED ENVIRONMENT 90 (high) degrees Fahrenheit in mid-summer. The Introduction frost-free period (at 32 degrees Fahrenheit) generally occurs for 120 days between late May and mid- This chapter contains a description of the natural September. The annual average total precipitation is resources, economic, and social conditions found in the nearly 12 to 16 inches, with 36 to 60 inches of total planning area and within the two Indian reservations annual snowfall. Temperatures will generally be adjacent to the planning area. cooler, frost-free periods shorter, and both precipitation and snowfall greater at the higher elevations, including the mountains in the southwest portion of the CBM Air Quality emphasis area. The air quality of any region is controlled primarily by Prevailing winds will occur from the southwest, but the magnitude and distribution of pollutant emissions local wind conditions will reflect channeling (mountain and the regional climate. The transport of pollutants and valley flows) due to complex terrain. Nighttime from specific source areas is affected by local cooling will enhance stable air, inhibiting air pollutant topography and meteorology. In the mountainous mixing and enhancing transport along the valley western U.S., topography is particularly important in drainages. Dispersion potential will improve along channeling pollutants along valleys, creating upslope ridge and mountain tops, especially during winter- and downslope circulations that may entrain airborne spring weather transition periods and summer pollutants, and blocking the flow of pollutants toward convective heating periods. certain areas. In general, local effects are superimposed on the general synoptic weather regime and are most important when the large-scale wind flow is weak. Existing Air Quality Although site-specific air quality monitoring is not Topography conducted throughout most of the CBM emphasis area, air quality conditions are generally good and well The coalbed methane (CBM) emphasis area is located within existing air quality standards, as characterized in the northern portion of the Powder River Basin of by limited air pollution emission sources (few the northwestern Great Plains Steppe in southeastern industrial facilities and residential emissions in the Montana. The Great Plains Steppe is a large relatively small communities and isolated ranches). physiographic province extending throughout most of Existing air quality throughout most of the analysis eastern Montana, Wyoming, and Colorado, as well as portions of western North and South Dakota, Nebraska, Kansas, and the Oklahoma panhandle. The topography of the CBM emphasis area varies from moderately What has Changed in Chapter 3 steep to steep mountains and canyons in the western Since the Draft EIS? portions, to rolling plains and tablelands of moderate relief (with occasional valleys, canyons, and buttes) in Chapter 3 describes the affected environment. The planning the eastern regions. Elevations generally range from area did not change between the Draft and Final EIS; about 3,000 to 7,000 feet above mean sea level, with however this chapter was changed to include a clearer mountain peaks rising to over 10,000 feet in the explanation of the current air quality and hydrologic southwestern portion of the CBM emphasis area. conditions, and to expand on the Geology and Minerals, and Native American sections. The Air Quality section was Climate and Meteorology enhanced with modeling data. Clearer text was added to the Hydrology section to explain the complex relationships Because of the variation in elevation and topography between ground and surface water. The Geology and throughout the CBM emphasis area, climatic Minerals section was expanded to include more maps of the conditions will vary considerably. Most of the area is emphasis area and a stand alone discussion of the geology. classified as a semiarid cool steppe, where evaporation The Native American section was expanded based on the exceeds precipitation, with relatively short warm completion of the Crow Tribe of Indians and Northern summers and longer cold winters. On the plains, Cheyenne Tribal Reports. Text throughout the chapter was average daily temperatures typically range between revised for simpler presentation. 5 to 10 (low) and 30 to 35 (high) degrees Fahrenheit in mid-winter, and between 55 to 60 (low) and 85 to 3-1 CHAPTER 3 Air Quality TABLE 3-1 ASSUMED BACKGROUND CONCENTRATIONS OF REGULATED AIR POLLUTANTS (µg/m3) Averaging Background National Ambient Air Montana Ambient Air Pollutant Time Concentrations1 Quality Standards Quality Standards Carbon monoxide (CO) 8-hours 6,600 10,000 10,000 1-hour 15,000 40,000 26,000 Nitrogen dioxide (NO2) Annual 11 100 100 1-hour 117 n/a 566 Sulfur dioxide (SO2) Annual 16 80 60 24-hours 89 365 260 3-hours 325 1,300 n/a 1-hour 666 n/a 1,300 PM 2.5 Annual 8 15 n/a 24-hour 20 65 n/a PM 10 Annual 30 50 50 24-hour 105 150 150 Source: Argonne (2002) Notes: 1 Background numbers are from Montana DEQ (MDEQ 2002) Modeling protocol (Argonne 2002) µg/m3 = micrograms per cubic meter n/a = not applicable PM10 fine particulate matter less than 10 microns in effective diameter PM2.5 fine particulate matter less than 2.5 microns in effective diameter area is in attainment with all ambient air quality • Dust (particulate matter) generated by vehicle standards, as demonstrated by the data presented in travel on unpaved roads and windblown dust from Table 3-1. However, three areas have been designated neighboring areas and road sanding during the as federal nonattainment areas where the applicable winter months. standards have been violated in the past: Lame Deer (PM10—moderate) and Laurel (SO2—primary), • Transport of air pollutants from emission sources Montana; and Sheridan, Wyoming (PM10—moderate). located outside the region. Anticipated existing contributors to pollutants within As part of the Air Quality Impact Assessment – the region include the following: Technical Support Document (Argonne 2002), • Emissions from oil and gas developments, e.g., monitoring data measured throughout southeastern natural gas-fired compressor engines (primarily Montana and northeastern Wyoming were assembled carbon monoxide [CO] and oxides of nitrogen and reviewed. Although monitoring is primarily conducted in urban or industrial areas and may be [NOx]) relatively higher than expected in the rural areas of the • Coal mining state, the data is considered representative of existing background air pollutant concentrations throughout the • Coal-fired power plants CBM emphasis area. These values, presented in Table 3-1, reflect conditions where existing air pollutant • Gasoline and diesel vehicle tailpipe emissions of sources (e.g., range fires, agricultural operations, etc.) combustion pollutants (volatile organic may be impacting ambient air concentrations and so compounds [VOC], CO, NO , fine particulate x were deemed to be reasonable for use to define existing matter less than 2.5 microns in effective diameter background conditions in the air quality impact [PM ], inhalable particulate matter less than 2.5 analysis. The assumed background pollutant 10 microns in effective diameter [PM ], and 10 concentrations are below applicable National Ambient sulfur dioxide [SO ]). 2 Air Quality Standards (NAAQS) and applicable 3-2 CHAPTER 3 Air Quality Montana Ambient Air Quality Standards (MAAQS) for Table 3-2 shows the relevant ambient air quality all pollutants and averaging times, as shown in the standards and PSD increment values. table. This NEPA analysis compares potential air quality impacts from the proposed Alternatives to applicable Regulatory Framework ambient air quality standards and PSD increments, but The National and Montana Ambient Air Quality comparisons to the PSD Class I and II increments are Standards set the absolute upper limits for specific air intended to evaluate a threshold of concern for pollutant concentrations at all locations where the potential impacts, and do not represent a regulatory public has access. The analysis of the proposed PSD Increment Consumption Analysis. Even though Alternatives must demonstrate continued compliance most of the development activities would occur within with all applicable local, state, tribal, and federal air areas designated PSD Class II, the potential impacts on quality standards. Montana’s ambient standards are not regional Class I areas are to be evaluated. The applicable within the reservation but apply to adjacent Montana DEQ will perform the required regulatory areas off the reservation. Finally, although the U.S. PSD increment analysis during the new source review Environmental Protection Agency (EPA) recently process. This formal regulatory process will include analysis of impacts on Class I and II air quality areas revised both the ozone (8-hour) and PM2.5 NAAQS, these revised limits will not be affective until the by existing and proposed emission sources. The Montana State Implementation Plan (SIP) is formally activities are not allowed to cause incremental effects approved by EPA. greater than the stringent Class I thresholds to occur inside any PSD Class I Area. Stringent emission Given most of the CBM emphasis area’s current controls (BACT – Best Available Control Technology) attainment status, future development projects and emission limits may be stipulated in air quality (including any proposed Alternative) which have the permits as a result of this review, or a permit could be potential